1. Field of the Invention
This invention relates to a door operator, more particularly to a door operator for a fireproof door.
2. Brief Description of Prior Art
Generally, the door operator used in a fireproof door is classified into two types depending on its operational mode: one is a failsafe mode and the other is a non-failsafe mode. In the case of the failsafe mode, a brake is immediately released by a brake device so as to shut the fireproof door in the absence of electrical power regardless of the reason of power failure. If fire breaks out in the presence of electrical power, the power is cut off by, for example, smoke detectors, temperature sensors or other fire detecting devices, or is cut off mechanically by a fusible link device which is molten at a high temperature in the fire in such a manner that the brake is released, and the door curtain shuts the fireproof door by its own weight. In this mode, the flame or escape of dense smoke can be blocked instantly when the fire occurs, if the cause of power failure is a fire indeed. Therefore, the main feature of the failsafe mode is more active for fire prevention. However, if the cause of the power failure is not a fire, a manually operating means has to be used for driving the door operator to open the door so as to maintain regular access for personnel.
On the other hand, in non-failsafe mode, the brake device is still maintained in a brake-actuated state without closing the fireproof door immediately in the absence of electrical power, regardless of the reason of power failure. Only if the occurrence of a fire is definitely confirmed by, for example, smoke detectors, temperature sensors or other fire detecting devices, a current transiently supplied from a reserved power source such as a capacitor, a battery or the like is supplied to the brake device for releasing the brake for a short period of time, or a fusible link is molten at a high temperature for mechanically actuating the brake device so as to release the brake, in such a manner that the door curtain falls down and shuts the fireproof door by its own weight. In this mode, the main advantage is that no inconvenience is encountered for personnel regular access is the main advantage, if the fire is not the cause of power failure. However, if the power failure is caused by a fire, and if the fire point is remote from the fire detecting devices or the fusible link, it is impossible to close the fireproof door immediately. Therefore, this mode is less safe for fire prevention.
Some documents associated with a failsafe mode door operator of a fireproof door have been proposed, such as U.S. Pat. Nos. 5,673,514 and 5,893,234 in which two electromagnets are used to maintain the brake-actuating state in the presence of electrical power, or to release the brake immediately so as to close the fireproof door in a power failure condition. The structure thereof is very complicated and has a large volume. On the other hand, a lot of documents concerning non-failsafe mode door operator of fireproof door such as U.S. Pat. Nos. 5,203,392 and 5,386,891 are disclosed, in which manual operation has to be conducted by switching operation mode, or a chain disk is rotated by pulling an endless chain and meanwhile the brake is released so as to rotate the rotary shaft. Thus, there is still room for further improvements on the implementation and the structure of a door operator.